When most people think of think of sexual orientation, they think of it as meaning whether a person is straight, gay/lesbian, or bisexual—and then they usually ignore bisexual. One widely used model for sexual orientation—the Kinsey Scale—uses something like this, placing exclusive heterosexuality at one end of a line and exclusive homosexuality at the other end, with varying combinations in the middle. This has two main problems. First, bisexuals are half of one thing and half of another, but not wholly anything. Second, it has no way of accounting for the fact that asexuals exist. They don't fit anywhere.
In the late 70’s a University of Kansas Psychology Professor, Michael Storms, proposed a different model, putting heterosexual attraction on one axis, and homosexual attraction on another. His motivation for this was a similar model recently proposed for understanding masculinity and femininity.
Traditionally, these had been understood on a model similar to the Kinsey scale—Masculine was at one end; feminine was at the other, androgynous was in the middle, in varying combinations of masculinity and femininity. Some people had objected to this: if someone is more masculine, that doesn’t necessarily mean they are less feminine. Some people are very masculine and very feminine (androgynous); some people are not particularly masculine or feminine (undifferentiated). A linear model groups these people together. To deal with this, researchers put these on two different axes: this allowed made it possible to distinguish between the “androgynous” and “undifferentiated” categories.
Storms applied a similar approach to sexual orientation, suspecting that the Kinsey Scale would also combine people with sexual attraction to both sexes and to neither into the same category since both groups presumably lacked gender preference in sexual partners. He then did a study to determine which model better described bisexuals: do bisexuals have sexual attraction toward people of the other sex at similar rates as heterosexual and towards people of the same sex at similar rates as homosexuals (as in his model), or was it about half-and-half (as on the Kinsey Scale)? His study indicated the former to be true. Unfortunately, not many studies since Storms have used this model, although some have shown interest in it.
One benefit this Storms’ model has for helping us to understand asexuality is that it is a model of sexual orientation that includes asexuality rather than leaving it an inexplicable anomaly—asexuals are people who experience levels of sexual attraction towards people of the other sex as frequently as homosexuals, and towards people of the same sex as frequently as heterosexuals: little to none. Another important point is that this model’s definition is a little different than the standard AVEN definition. Instead of defining asexuals as “people who do not experience sexual attraction,” it defines them as “people who experience little or no sexual attraction.”
There is another prediction that this model makes that Storms didn’t seem to recognize, but it’s well known in asexual circles to be true: there is no clear line that divides asexuals and the non-asexuals. Some people have never experienced sexual attraction; others have felt it but only towards one or two people, ever. Still others feel sexual attraction, but only a couple times a year or experience it so little, they have no desire to act on it. Where do we draw the line between who is and who isn’t asexual? I have no idea. Neither does anyone else. This is exactly the situation Storms’ model tells us we should expect to find.